1. Field of the Invention
The invention relates generally to a system for welding identically convoluted metal surfaces and, more particularly, a combination for clamping a welding apparatus to the convoluted surfaces to guide and control the welding apparatus in order to weld identically convoluted surfaces in accordance with predetermined conditions without regard for the orientation of the surfaces.
Since the convoluted sheets are intended to be used to construct a relatively large, completely enclosed, self-supporting structure requiring welding the sheets together from the inside, the system must be relatively small and light-weight and capable of performing the welding at every possible angle. Also, the system is required to perform the welding without aid of physical support with the exception of the convoluted surfaces adjacent the welding seam.
2. Description of the Prior Art
Control systems for performing automatic welding operations are known in the art. Guiding a welding apparatus in response to changes in the vertical and/or horizontal position of the welding seam or the vector result thereof is shown, for example, by U.S. patent application Ser. No. 874,153 filed Nov. 5, 1969. In such instances, the welding apparatus and workpiece move relative to one another to effect the welding of a seam or line on the workpiece. A probe detects variations in the vertical and/or horizontal position of the seam in space and generates a signal which is utilized to position the welding torch at the vectorial result of such changes.
The apparatus of the present invention also varies the positioning of a welding apparatus automatically in response to changes in the spacial location of the welding seam. In this instance, however, the relative position of the welding apparatus perpendicularly with respect to the major plane of the convoluted sheets is one of the changes which must be effected with regularity. Varying this dimension with respect to a workpiece having a convoluted surface represents a considerable divergence from the standpoint of complexity and practicality of an automatic welding device.
Detecting changes in the relative position of the welding apparatus normal to a major plane, particularly where the deviations are considerable, such as the convoluted surfaces in the metal used in large shipping containers for liquified gas, fuel, and the like, and using the information obtained as a result of such detection to control the positioning of the welding apparatus, has proven difficult. Many attempts to automatically weld such containers have been made. None has been successful.
The problems of designing a system such as is necessary to effect the desired welding of sheets having convoluted surfaces are increased by the addition of the requirement that no filler material be utilized in welding the sheets. That is, two overlapping, convoluted sheets are heated to the point of melting and fusing the two, without adding any additional metal material. In a case such as this, the exact positioning of the welding apparatus is extremely important. If heat from the welding apparatus is applied at a point other than the overlap of the sheets, a burn-through is possible. Even if the mispositioning does not burn through the sheet, the desired penetration of the welding is dependent upon the proper positioning of the welding apparatus.
Still another consideration in the design of a system capable of welding convoluted sheet surfaces such as those of the present invention, involves varying the speed at which the welding apparatus travels in the direction of the weld. This becomes important due to the effects of a volume of air being present at the opposite side of the sheet in the areas of the convolutions. Such a volume of air is liable to cause a heat build-up in the sheets and, thus, a burn-through. While the problem of welding on the convolutions requires an increase in speed or decrease in current applied to the welding apparatus upon the approach thereto and initial welding thereof, the complexity and rate of change in direction of the convolutions necessitates a converse correction of the variables, after welding of the convolution is initiated and upon completion of passage thereover.